Raspberry Pi Model B Voltage Limits


3 posts
by KoviRobi » Sat Jun 23, 2012 2:08 pm
Hi!

Sorry, if this has been asked, I tried searching for voltage, but it came back with robotics results.

First of all, my set-up:
* 1 Amp 5 Volt HTC charger (though the CE mark looks like China Export: http://www.raspberrypi.org/archives/996 )
* HDMI Output
* Ethernet Cable (I believe Cat5, but there are no markings on the cable)
* And of course, a Raspberry Pi Model B

My question is: During boot, the TP1 TP2 voltage is ~4.9 volts, but by the time it has booted to a prompt, it increases to ~ 7.1 volts. Nothing is smoking, but I am interested, to see if this is in working range, as http://elinux.org/RPi_Hardware#How_Can_ ... dequate.3F cites 4.75 and 5.25 volts.

Thank you,
Kovacsics Robert
Posts: 2
Joined: Sat Jun 23, 2012 1:47 pm
by dom » Sat Jun 23, 2012 2:31 pm
That is way out of spec and could cause damage.

Now one possibility is there is something wrong with the meter and it's not really that high.
Note the Pi has no way of increasing the voltage given, so if the reading really is that high then it sounds like the charger is faulty. Do not use it.
Just to rule anything else out, unplug any HDMI/ethernet/USB cables before measuring.
Raspberry Pi Engineer
Raspberry Pi Engineer
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Location: Cambridge
by KoviRobi » Sat Jun 23, 2012 3:03 pm
Ok, I have plugged everything out, and then measured the voltage, here are my results (the Raspberry Pi has been switched off for a while).

* All (except power) unplugged, voltage stays ~ 4.75
* I plug in HDMI, voltage starts to creep up, and does not seems to level, so I switch it off, when voltage reaches 5.25 volts
* I switch it on with a different HDMI cable, voltage is up to about 5.7 volts, I switch it off
* I switch it on with only power cable, voltage is ~6.4, I switch it off.
* It is switched off, but voltage is decreasing from 0.75 volts (possibly due to the capacitor?)

I will test with a different volt meter, in school on Monday, and a different MicroUSB cable, when it arrives. I will also test it again, when the switched off voltage is zero, without the HDMI cable, to double check if it really does not increases without it.

Thank you for your quick reply!
Posts: 2
Joined: Sat Jun 23, 2012 1:47 pm